It is well known in the prior art to manufacture tire components from elastomeric sheets of rubber which are then cut to length and lapped or butt spliced onto a cylindrically shaped building drum. The tire building drum is then expanded radially in the center and the ends are drawn in axially to shape the tire into a torus. Belts of cord-reinforced layers and a strip of tread rubber are applied over the crown of the green carcass to form a “green” or unvulcanized tire assembly. The finished tire assembly is then placed into a tire mold and cured in a process called vulcanization to make a tire.
Since the tire components are assembled flat onto a cylindrical tire building drum and then expanded into a toroidal shape, each component has to be placed in tension or compression prior to being molded. This stretching of the various parts causes slippage between the various rubber parts as the components heat up during vulcanization. Attempts to minimize the slippage of the various parts have been attempted. Another disadvantage is that the tire has components which are spliced, and which contribute to tire nonuniformity.
Tire manufacturers have been increasingly focusing their efforts on eliminating tire nonuniformities. More recently, tire manufacturers are making tire components from a continuous strip of unvulcanized rubber. A thin, narrow strip of unvulcanized rubber is circumferentially wound multiple times onto a rotating drum or toroid shaped core, wherein the strips are successively layered or stacked in order to form the desired shape of the tire component. See for example, U.S. Pat. Nos. 6,372,070 and 4,963,207. The strip of rubber is typically extruded directly onto a tire building drum or toroidal-shaped core using an extruding device. Alternatively the strips may be formed from calendering and then conveyed to the tire drum or core.
This strip lamination method of forming tire components has the advantage of eliminating splices because the annular tire component is typically formed of one continuous strip. Strip lamination has the further advantage of allowing flexibility in manufacturing, since the tire component profile may be changed from tire to tire. However, there are several disadvantages to strip lamination. First, trapped air or air pockets may be formed in between the strips, creating gaps in the finished tire component. A second disadvantage to the strip lamination is that the contour of the tire component is an approximation due to the stacking of the strips which have a fixed geometrical shape. Further as a result of the stacking, the outer surfaces of the tire component are not smooth. The component contour typically has staggered top and bottom surfaces which can cause surface defects commonly referred to as “lights” or discolorations. A third disadvantage is that the strips need to be stitched to the drum or core using a pressure roller or stitcher, and the rubber tends to stick to the roller. A further disadvantage is that since the component is formed from multiple strips, it is only an approximation of the desired shape.